In the related art, a liquid crystal projection device for projecting a modulated image on a screen by using a display device is well known, and in the liquid crystal projection device, the display device is used to modulate three different monochromatic light beams, such as, red (R), green (G), and blue (B), and obtain the modulated image. In order to increase the resolution of the image projected on the screen, it is required that the liquid crystal projection device be of a high resolution. For this purpose, it has been attempted to increase the number of pixels of a liquid crystal display device, or form the images in plural screens with plural projectors, or shift green pixels by half pixel pitch to obtain effects equivalent to doubled pixel numbers.
However, when the number of pixels is increased, for example, in a transmission-type liquid crystal display device, the area of the open area of each pixel decreases, and the projection luminance becomes insufficient. When using plural projectors to display the images on plural screens, it is difficult to obtain smooth connection between the images on adjacent screens. When shifting the green pixels by half pixel pitch to obtain the double-pixel-number effect, because the R, G, B light in the whole band is projected on the screen to form an image by using only one projection lens, and because of the monochromatic aberration of magnification of the projection lens, different monochromatic images do not have precisely the same size, thus it is difficult to form an image of a high resolution and obtain a sufficiently large contrast ratio.
To solve this problem, a display technique is proposed in which a pixel-shift element is used to switch the light path quickly, thereby, increasing the number of pixels apparently, and thus realizing high-resolution display. This technique is promising because it is capable of easily realizing high-resolution display.
For example, in the related art, it has been attempted to combine the light path shift technique with a so-called “color sequential technique”. In the color sequential technique, color light beams, for example, of the three primary colors, are generated sequentially at a high speed in a time-division manner for illumination, thus, monochromatic images are displayed sequentially on the screen corresponding to the illumination monochromatic light, and resultantly, it looks as if color images are being displayed. This technique is promising because it can be realized with a compact and inexpensive device. In the related art, when combining the above two techniques, however, a light valve of very high-speed response is required.
For example, as a simplified calculation, since three sub-frames are required for the three primary colors, R, G, B, respectively, the total required number of sub-frames equals the total number of times of pixel-shift operations multiplied by three (the number of sub-frames for R, G, B). For example, assume the number of times of the pixel-shift operations is two (that is, pixels are shifted to two different positions in one image frame), the required number of sub-frames equals 2×3=6, that is, it is necessary to display 6 sub-frames. In other words, it is necessary to update the image data applied on a light valve at least 6 times in each image frame, and the pixel shift element needs to perform switching three times.
It is reported that development is being made on such a high-speed light valve, but a device ready for mounting in a product has not been manufactured.
Instead of the combination of the pixel shift technique and the color sequential technique, in the related art, it has also been attempted to simply increase the pixel number of a light valve to increase the resolution of the display device. In this case, however, the size and cost of the light valves increase.
In addition, in the related art, it has been proposed to increase the number of the light valves to increase the resolution of the display device. For example, a liquid crystal projection devices have been disclosed which are able to display images of high resolution and a high contrast ratio in Japanese Laid Open Patent Application No. 2003-322854 (hereinafter, referred to as “reference 1”).
FIG. 34 is a diagram illustrating a configuration of the liquid crystal projection device in the related art, as disclosed in reference 1.
In the liquid crystal projection device 100 illustrated in FIG. 34, there are two reflection type liquid crystal display elements 115, 116, which are for use of the green color; incident light is projected so that pixel shift is performed in an inclined direction; thus the resolution of the green image, which has high relative visibility, is doubled, thereby realizing a high resolution display.
In addition, Japanese Laid Open Patent Application No. 2003-322908 (hereinafter, referred to as “reference 2”) discloses a projection system which includes a transmission type liquid crystal display panel composed of four transmission type liquid crystal display elements.
However, in reference 1 and reference 2, two green display panels are employed and are arranged such that respective images formed by the two green display panels are shifted by a distance less than a pixel pitch to double the pixel number. As a result, the number of panels increases, and this causes increased cost of the display device.